Antenna selector



2 Sheets-Shee'l 1 J. B. MOORE ANTENNA SELECTOR Fild Nov. 16, 1928 June l1, 11935.'

June l1, 1935.

J. B. MOORE ANTENNA sELEToR Filed NOV. 16, 1928 2 SheebS-Sheet 2 sfu .551,2 552: 3

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.mirra/e3 114' Silit/a 2 ||||I|| fr 3 INVENTOR JOHN B. MOORE ORNEY Patented June 11, 1935 UNITED ,STATES ANTENNA ssnsc'rolr` John B. Moore, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application November 16, 1928, Serial No. 319,768

12 claims.

This invention relates to diversity reception, and more particularly to a method and means for selecting from a plurality of antennas that antenna which is supplying the strongest signal.`

Short wave signals are subject to fading which varies both in frequency and degree in an unpredictable manner. Inasmuch as the fading at any instant may differ very widely at geographically spaced points, or in different planes of polarization, it has been suggested that a receiving station be equipped with a number of antennas having different fading characteristics, the energies collected by which are'fed to a single signal responsive means.

Experience has shown that high frequency energy iiuctuates not only `in intensity but also in phase, and that there may be considerable relative phase fluctuation on the different antennas. This phenomenon makes it impossible to ldirectly combine the audio frequency energies, for the energies may as often `be in phase opposition as in like phase. To overcome this difliculty it has been suggested to equip each of the antennas with a separate receiver, and to combine the energies only after rectification, and'this, in the case of code signals, has proven an apt solution.

However, I have found that in the case of speech telephony, or other speech-simulating signals, Where the transmission energy is radiated in the form of a carrier and side bandathere is a relative difference in the phase fluctuations of closely adjacent frequencies, such as side band and carrier frequencies, even at one antenna, just as there is between carriers of like frequency at different antennas. This causes similar phase fluctuations in the beat of the carrier and side bands, for if of two beating waves one is kept constant in phase, while the other is shifted in phase, their beat is equally shifted vin phase.

This may readily be understood by visualizing two beating radio frequency Waves of slightly different frequency, which have an Lenvelope which is a maximum Where the Waves are cophasal, and which gradually drops oif to a minimum where the waves are in phase opposition. Now if the phase of one of these waves is kept constant While the phase of the other is shifted 180 degrees the Waves will be in phase opposition Where before they were cophasal, so that the envelope will be a minimum Where before it was a maximum, and Where the waves Were in phase opposition they now will be cophasal, so that the envelope will be a maximum Where before it was a minimum, and, therefore, in effect the envelope too has been shifted 180 degrees in phase.

(Cl. Z50-20) Because of the foregoing considerations it fo-l- `lows that although the carrier and side band energies experience only radio frequency differences in phase, these differences are transferred to the detected or audio frequency energies, so that it vis as impossible to combine the detected energies as it is to directly combine the originally collected radio frequency energies. y

The primary object of my invention is to overcome this diiculty, making possible the application of diversity reception to overcome fading of speech-simulating signals, and for this purpose I collect signal energy on a plurality of antennas so geographicallyv spaced, or so altered in `plane ofpolarization, or otherwise changed, that the 15 fading characteristics thereat usually differ, as heretofore, but I then feed the collected energy to a receiver from only that point of collection or antenna at which the collected energy is a maximum, instead of from all of the antennas at once. l.

With' the usual type of diversitysystem, even if applied merely to code signals, the received energy is apt to vary Vbetween the extremes of `almost complete fading at all of the antennas `to no fading at any of the antennas. To overcome this it hasbeen suggested to employ a volume control with each antenna for varying the gain in the amplifier coupled thereto. Such an arrangement suffers from the disadvantage `that the increased gain given an amplifier of an antenna at which fading is prevalent increases' the noise level in the outputof that ampliiier, and `therefore in the combined output of the-entire system. Furthermore, in the case of speech-simulating signals, in the event of fad.- ing of the carrier and not of the side bands at an antenna its amplifier is given increased gain, as a result of Which'the beat between the `side bands is unduly amplified before being combined 40 withthe output from the other antennas, thereby creating augmented distortion.

To overcome the foregoing difficulties is a further object of my invention, which I fulfill by the process which I have already suggested, namely, feeding the collected energy to the receiver from only one of the antenas at a time. This inherently provides considerable volume control, forlthe condition of no fading at any of the antennas 4does not create a powerful sig- 50 nalequal to the integral of the several signals, because only one instead of all of the antennas is connectedto the receiver. Furthermore, among all of the several antennas employed there is almost always; one having a fairly strong signal,

and the automatic coupling of the receiver tothis antenna amounts, practically, to automatic volume control.

To provide volume control within still narrower limits, so as to obviate the effect of partial fading of even the maximum signal, I combine automatic volume control with the receiving system which I have already described.

My invention is more completely described in the following specification which is accompanied by drawings in which Figure 1 is a wiring diagram for an arrangement with two antennas; and Figure 2 is an arrangement employing a'greater number of antennas. I

Referring to Figure 1 there are two geographically spaced antennas 2 and 4, which are coupled by transmission lines E and 8 to radio frequency amplifiers [l and l2. The output from these ampliiiers is fed to means to heterodyne the received radio frequency energy to energy of intermediate frequency, indicatedrby the rectangles |4 and IB, and which may comprise separate oscillators and heterodyne detectors, or autodyne circuits in which the .same tubeacts as an oscillator tube and as a. heterodyne detector tube. The intermediate frequency is amplified in suitable in termediate frequency amplifiers I8 and 2t, the amplified outputs from which are detected in de tector tubes 22 and 24, across the anode circuits of which there are connected the filter sections Z6 and 28 for lay-passing the radio frequency components of the rectified energy. The remainder of the anode to ground circuit includes sources of direct anode potential 30 and 32 and volume control impedances 34 and 36. The potential across the impedance 34 is applied through the leads 38 and 40 to the control electrodes of the tubes in the amplifiers Il)l and i8, and also, by way of the leads 38 and 42, to the control electrode of the tube 44 of the pair of tubes 44 and 46. The potential across the impedance 36 is applied by way of leads 48 and 50 tothe control electrodes of the vacuum tubes in the amplifiers 2 and 2U, andgalso, through the leads 48 and 52, to the control electrode of the tube 4E. The resistances 39 and 49 are provided in series with the condensers 31 and 4'! in `order to form electrically slow circuits for volume in turn depends upon the potentials across the impedances 34 and 36, which, of course, vary in accordance with the strength of the signals received by the antennas 2 and 4. The differential of the anode currents may be applied directly to the 'coils of a differential relay, the armature of which is arranged to act as a switch to connect a utilization circuit to that'one ofthe impedances Maud 36 through which the greater signal energy is flowing. However, insuch case the relay would have to accommodate itself to wide ranges in variation of current, and therefore could not be quite so sensitive as the arrangement which I prefer to employ and which is next described, but it should be understood that either arrangement is responsive to the differential of the anode currents, the one directly, and the other indirectly. The anodes of the tubes 44 and 4t are coupled to anode impedances lil and l2, to the junction of which a source of anode potential i4 is connected. The differential of the anode potentials is applied to the input circuit of a tube and the coupling may include a resistance 18 to prevent the flow of appreciable grid current in tube i@ should the anode of tube 44 become considerably more positive than that of tube 46, and to give a more nearly definite maximum to the anode current ow in tube 76, which in general depends upon the differential of the anode potentials of the tubes 44 and 45, and which is utilized in the coil 8B of a differential relay 82. A constant now of current from a source S4, nicely adjusted by a resistance 85,' is fed through the opposed coil 88 of the relay. The adjustments are made such that with equal signal strength on antennas 2 and 4 the current through the relay coil 8o counteracts that through the relay coil 88, but therconstruction of the relay is such that it will then rest at either contact with equal facility, but will not so centralize itself as to open circuit both contacts.

It will be understood that not onlyv might the relay 82 be connected directly in the anode circuits of the tubes 44 and 4Q, but also the arrangement just described, including theV tube 75 and the source 84, might be connected so that the differential of the potentials across the impedances 34 and 36 is applied directly tothe control electrode of the tube 'f5 without the intermediate use'of the pushpull tubes d4 and 45, but these are desirable because the voltage ampliiication obtained by their use permits the relay to function on a very small difference in signal level, which makes the change over imperceptable to the listener.

In order to abstract signal energy for utilization there are coupled to the impedances 34 and 3G amplifier tubes 9U and 92, through grid bias blocking condensers S4 and 96. The anode circuits of these tubes include the coupling transformers 98 and |60, the primaries of which are connected together and to a source of anode potential |82. One terminal'of the secondaries of the transformers S8 and |09 are connected together and to the primary of transformer |04, while the other terminals are led separately to the opposite contacts of the relay 82, as shown. The armature of the relay is then connected to the opposite terminal of the primary of thetransformer |04, so that the relay, in contacting with one side or the other, effectively couples either of the amplifier tubes and 92 to the transformer |34. The secondary of the transformer iilfi may be the input coil of a pushpull amplifier stage |06, the output from which is fed over a line |68 to acoustic or picture translating means, or a re- -broadcasting station, or other suitable means to utilize the signal energy.

In the foregoing arrangement it should be understood that the receivers need not be heterodyne receivers, as shown, and that if they are heterodyne receivers, the volume control leads il and 5G may be connected to either the high frequency or the intermediate frequency ampliers alone, as well as to both, as shown, and that, furthermore, volume control leads 45 and 553 are not at all essential to the practice of the invention in its broadest aspect, involving merely antenna selection, though volume control is a useful auX- iliary in practice.

If it is desired to employ more than two antenllas, and at the same time to retain the use of .gioca-12e tennas, is indicated in Figure 2, in which there are a plurality vof .antennas ID, I2` and I4,`

either geographically spaced, Iorf` in` different planes of polarization, or otherwise given different fading characteristics, whichr are coupled by means of transmission lines |20,` |22 'and |24, to receivingsets |30,|32, and |34, as shown. The rectified output from receiversl |30 and |32 is applied to a differential relay selector |36, while the rectified outputs from the receivers |32 and |34 are fed to another differential relay selector |38. The volume of energy from receivers |30 and |34 is yet to be compared, and these are applied toa third differential relay selector |40, the contacts of which are connected, as shown, to the armature of the relays |36 and |38, the contacts of which in turn are connected to the signal outputs from the various receivers |30, |32 and |34. Inasmuch as these outputs are preferably taken through separate amplifiers, they have been indicated in Figure 2 as coming from separate rectangles |52 and |54, but it should be understood that these are respectively coupled to the receivers |36, |32 and |34, just as was indicated in Figure 1. Through the operation of the three relays |36, |38 and |40, the armature of the relay |46 is ultimately coupled, through intermediate circuits, of course, to that antenna having the strongest signal, and this is then connected, along with the common lead |56 fromthe signal ampliers |56, |52 and |54, to a line |58, intermediately through a further amplifier |60, should this prove desirable. As before, the line |58 is led to any suitable utilization means.

I claim:

1. The method of reception which includes collecting signal energy on three geographically spaced antennas, separately rectifying the collected signal energies, comparing the rectified energies obtained from two of the antennas and selecting the greater, comparing the rectified energies obtained from another two of the antennas and selecting the greater, comparing the rectified energies from the remaining two and using them to select the greater of the selected energies, and utilizing the finally selected energy. i

2. The method of reception which includes collecting the received energy on a plurality of geographically spaced antennas, separately amplifying the received energies, separately rectifying the amplified energies, controlling the gain in the aforesaid step of amplification in response to the volume of the rectified energies to obviate the effect of partial fading, and selecting the maximum of the rectified energies for utilization.

3. A receiving system for the reduction of fadingr of high frequency signals comprising a plurality of antennae so geographically spaced that the fading characteristics thereat usually differ, means individual to each antenna for automatically volurne controlling energies derived therefrom, a receiver, and automatic switching means responsive to the differential of the volume controlled energies collected on the antennas for coupling the receiverto that antenna only at ywhich the collected energyis a maximum.

4'. A diversity receiving system for overcoming the effectief fading of speech-simulating signals transmitted on a high frequency carrier, in spite .r1 iof fluctuations inthe relative phase of closely ad- 'jacent frequencies such-as sideband and carrier frequencies, comprising a plurality of antennas having different fading characteristics, means in- `dividual to each antenna to volume control the energy collectedon each antenna, a receiver, and differential relay switching means responsive to lthe differential of thegvolume controlled energies Vderived from energies collected by the antennas of antennas of relativelypdifferent fading characteristics, a plurality of detectors coupledthereto, means individual to each antenna to automatically volume control energies collected thereby, a utilization circuit, and switching means responsive to the differential of the detected automatically volume controlled energies for coupling the utilization circuit to that detector at which the rectified automatically volume controlled energy is a maximum.

6. A receiving system comprising a plurality of geographically spaced antennas, a plurality of detectors coupled thereto, means individual to each antenna circuit for automatically volume controlling energies collected thereon, a utilization circuit, and switching means responsive to the differential of the detected automatically volume controlled energies for coupling the utilization circuit to that detector at which the automatically volume controlled rectified energy is a maximum.

'7. A receiving system comprising a plurality of geographically spaced antennas, a plurality of detectors coupled thereto, means to select the greater energy of the energies collected by the antennas considered two at a time, means to select the greater of the selected energies, until the maximum energy has been selected, and means to utilize the maximum energy.

8. A receiving system comprising three geo-` graphically spaced antennas, a plurality of detectors coupled thereto, means to compare the detected energies obtained from two of the antennas and to select the greater, means to compare the detected energies obtained from another two of the antennas and to select the greater, means to compare the detected energies from the remaining two antennas and to utilize them to select the greater of the selected energies, and means to `utilize the finally selected energy.

9. A receiving system comprising a plurality of geographically spaced antennas, means to separately amplify the collected energies, means to separately rectify the amplified energies, volume control means for controlling` the gain in the amplifiers in response to the volume of the rectified energies in order to obviate the effect of partial fading, and means to select the maximum rectified energy for utilization.

l0. A receiving system comprising a plurality `of geographically spaced antennas, means to separately rectify the energies collected thereby, an impedance in each of the detector circuits, a pair of electron emission tubes, means to apply the potential caused by the flow of the rectified currents through said impedances to the control electrodes of the pair of tubes, means to combine the anode currents of the tubes differentially', a utilization circuit, and a differential relay responsive'to the differential of the anode Acurrents for connecting the utilization circuit to that detector circuit through which the maximum signal energy is flowing.

11. A receiving system comprising a plurality of geographically spaced antennas, a plurality of ampliers coupled thereto, a plurality of detectors coupled to the ampliers, an impedance in each of the detector circuits, a pair of electron emission tubes, means to apply the potential drop across the impedances tothe control electrodes of the amplier tubes in order to control the gain therein and to the control electrodes of the pair of electron emission tubes, means to combine the anode currents of the pair of tubes differentially, a utilization circuit, and a differential relay responsive to the differential ofthe anode currents for connecting the utilization circuit to that detector'circuit having the maximum signal energy. Y

12. A receiving system comprising a pair of geographically spaced antennas, a detector coupled to each of said antennas, an impedance in each ofthe detector circuits, a pair of electron emission tubes, means to apply the potential drops across the impedances to the control electrodes of the tubes, means coupling the anode circuits of the tubes diierentially and to the control electrode of a third tube, a differential relay, means coupling one of `the coils of the relay to the anode circuit of the third tube, a source of constant current for the other coil of the relay, a utilization circuit, and a switch actuated by the relay for coupling the utilization circuit to that detector impedance across which the potential drop is greater.

JQHN B. MOORE. 

